(a) Technical Field
The present invention relates to a manifold device of a fuel cell stack, and more particularly, to a manifold device of a fuel cell stack, which prevents flooding due to liquid by increasing the temperature of gases supplied into a stack using stack heat and thus completely vaporizing liquid included in gases.
(b) Background Art
Generally, hydrogen is supplied to the anode of a fuel cell stack as a fuel. For improvement of hydrogen utilization rate or reaction performance of the fuel cell stack, in the anode, an anode off gas that is discharged from the stack is recirculated into the fuel cell stack again. In particular, the anode off gas is mixed with hydrogen newly supplied from a fuel tank, and then is supplied into the stack. Hydrogen newly supplied from the fuel tank is hydrogen of an ordinary temperature (e.g., atmospheric temperature), which is in cold and dry (e.g., relative humidity ˜%) state. Additionally, the anode off gas discharged from the stack is of a substantially high temperature and humid gas which is heated to the operation temperature of the stack and is humidified by moisture back-diffused in the cathode. Accordingly, the mixed gas (e.g., newly supplied hydrogen+anode off gas) decreases in temperature compared to the anode off gas, and thus a substantial amount of liquid water is generated in the mixed gas.
Further, the gas introduced into the stack is mixed with newly supplied hydrogen and recirculating hydrogen by a recirculation apparatus such as an ejector or a blower, and then is supplied to the stack. In particular, the suction force of the ejector or the blower may also cause liquid discharged from the outlet of the stack to recirculate and flow into the inlet of the stack. Particularly in winter (e.g., colder weather months), since the temperature of the fuel tank is substantially low, the inflow of such liquid may cause substantial performance reduction (e.g., voltage drop of specific cells) of the stack.
More specifically, referring to FIG. 7, when water in liquid state flows into a fuel cell stack 10, liquid is introduced into cells disposed at the inlet of the fuel cell stack 10, and thus partial clogging may occur on anode channels of cells disposed at the side of the inlet, causing anode flooding and rapid reduction of the voltage (performance) of the cells at the side of the inlet.
Additionally, as shown in FIG. 7, when the inlet and the outlet of the anode are disposed at one side of the stack 10, there occurs a substantial flow rate difference (differential pressure) between a cell adjacent to the inlet and the outlet and a cell distant from the inlet and the outlet. In other words, cells adjacent to the inlet and the outlet have a rapid flow rate due to a shorter recirculation path, whereas cells distant (e.g., at a predetermined distance from) from the inlet and the outlet have a slower flow rate due to a longer recirculation path. Accordingly, when there is minimal liquid flowing into cells adjacent to the inlet and the outlet, water may be discharged at a rapid flow rate. However, for the cells distant from the inlet and the outlet, since liquid water in the anode channel is not substantially discharged, anode flooding may be caused. Additionally, since there is a heat loss in an end plate of the stack, excessive liquid exists in cells disposed at both ends of the stack compared to other cells. Accordingly, since more liquid exists in cells distant from the inlet and the outlet than cells inside the stack, it is more disadvantageous for cells distant from the inlet and the outlet to discharge liquid.
Furthermore, since cells distant from the inlet and the outlet are relatively low in hydrogen concentration compared to cells adjacent to the inlet and the outlet, the hydrogen concentration is non-uniformly distributed on respective cells. When water flowing into the anode channel of each cell is not substantially discharged, a catalyst or a catalyst support is permanently damaged. Generally, water accumulated in cells may be discharged by opening a purge valve of the anode and thus instantaneously increasing the flow rate of circulating gas, but in this case, a loss of a fuel is incurred. Typically, flooding in the cathode of the stack may be removed by increasing the supply amount of air.
The above information disclosed in this section is merely for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.